The proof of license label is the orange label, accompanying the installation media, that contains a 25-character product key. The words "Proof of License" appear on the label. The proof of license label cannot be purchased separately. Versions of the label prior to the release of Windows XP Service Pack 2 did not contain significant security features, such as the security thread, microprint, or the words "Proof of License," and are, therefore, not shown below.